Chiller water sampling device

ABSTRACT

A chiller water sampling device includes a pair of flow meters and a proportional valve to provide a constant flow rate of sample water containing peroxyacetic acid from a chiller to a mixing tank. Acid can be added to reduce the pH of sample water in the mixing tank to bring the pH within the operating range of a peroxyacetic acid sensor. The sensed level of peroxyacetic acid can be used to control further addition of peroxyacetic acid to the chiller.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the priority of U.S. ProvisionalApplication No. 62/585,639, filed Nov. 14, 2017, which is incorporatedby reference in its entirety herein.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to devices for monitoring the level ofbiocide in poultry plant chillers.

2. Brief Description of the Prior Art

Peroxyacetic acid is employed in food chillers, such as auger and dragtype poultry chillers, which are employed in processing plants to reducethe temperature of birds which have been defeathered, eviscerated andare otherwise ready for packaging. Poultry chillers are described, forexample, in U.S. Pat. Nos. 3,240,026; 7,281,384; 6,865,895; 9,271,509;all incorporated herein by reference. Various methods have been employedto reduce microbial activity in chiller water, which is typicallyrecirculated and cooled during recirculation. For example, U.S. Pat. No.4,849,237 discloses sanitizing poultry carcasses using ozonated water atlow temperatures. U.S. Patent Publication 2009/0208616 A1 discloses amultistage process for treating poultry processing water with chlorineand ozone. Peroxycarboxylic acids have been used to reduce microbialactivity in poultry processing. For example, U.S. Pat. No. 5,683,724describes a process for inhibiting microbial growth in aqueous foodprocess streams using a percarboxylated acid, such as peracetic acid.U.S. Pat. No. 9,414,609 discloses treating poultry carcasses with anequilibrium solution of peroxyacetic acid at an elevated temperatureprior to chilling. Peroxyacetic acid can be provided in the form of anequilibrium solution, or a non-equilibrium solution, such as disclosed,for example, in U.S. Pat. No. 10,081,784.

When peroxyacetic acid is used as an antimicrobial agent in poultrychillers, there is a need to accurately assess the level of peroxyaceticacid to ensure efficacious results.

SUMMARY OF THE INVENTION

The present invention relates to a chiller water sampling device. Thedevice includes a first line for fluid communication with a chiller,such that an aqueous sample can be delivered from the chiller to thedevice. The device also includes a first flow meter for sensing fluidflow through the first line; a diverter in fluid communication with thefirst line for dividing the fluid flow from the first line into a secondline and a third line; a second flow meter for sensing fluid flowthrough the second line; and a first valve for controlling fluid flowthrough the second line such that fluid flow from the device can bedischarged through the second line.

The device also includes a second valve for controlling fluid flowthrough the third line and a mixing tank for receiving fluid flow fromthe third line, as well as an acid storage tank in fluid communicationwith the mixing tank, and a first metering device for controlling fluidflow from the acid storage tank to the mixing tank. A first pH sensingdevice for monitoring the pH of fluid in the mixing tank is alsoprovided. The pH first sensing device generates a first signalresponsive to the pH of the fluid in the mixing tank, the first signalbeing applied to the first metering device for controlling fluid flowfrom the acid storage tank to the mixing tank. A fourth line fordischarging fluid from the mixing tank is also provided.

Further, a second pH sensing device for monitoring the pH of fluidflowing in the fourth line is provided, as well as a fifth line in fluidcommunication with the fourth line for discharging fluid from thedevice, and a third valve for controlling fluid flow through the fourthline. A sixth line in fluid communication with the fourth line fordischarging fluid from the device is also provided, as well as a fourthvalve for controlling fluid flow through the sixth line. The second pHsensing device generates a second signal for controlling operation ofthe fourth valve and a third signal for controlling operation of thefourth valve.

In addition, a first PAA sensing device for sensing the concentration ofperoxyacetic acid in fluid flowing in the sixth line is provided, thefirst PAA sensing device has an operating range, and provides a signalin response to the concentration of sensed concentration of peroxyaceticacid signal.

Preferably, the device further comprises a filter in the third line forfiltering non-fluid material from fluid flowing from the diverter to thesecond valve.

Preferably, the device further includes a seventh line for providingfluid flow to the third line, fluid flow through the seventh line beingcontrolled by a fifth valve, the seventh line being in fluidcommunication with the third line between the diverter and the secondvalve.

Preferably, the device also includes an overflow line, the overflow linebeing in fluid communication with the mixing tank for discharging fluidfrom the device, the overflow line being positioned on the mixing tankabove a predetermined fluid level in the mixing tank.

Preferably, the device also includes a second PAA sensing device forsensing the concentration of peroxyacetic acid in the sixth line.

Preferably, the device further includes an eighth line for providingfluid flow to the sixth line, the fluid flow in the eighth line beingcontrolled by a sixth valve, the eighth line being in fluidcommunication with the sixth line between the fourth valve and the firstPAA sensing device. Wash water can be provided through the eighth line.

Preferably, the first flow meter generates a first flow control signal,the second flow meter generates a second flow control signal, and thefirst valve is a proportional valve. Preferably, the device furtherincludes a controller for comparing the first signal and the secondsignal, and for generating a control signal for the proportional valve,such that the flow through the third line is maintained at apredetermined flow rate.

The present invention also provides a system for controlling theconcentration of peroxyacetic acid in the contents of a chiller, thesystem comprising the chiller water sampling device, a source ofperoxyacetic acid, a metering pump for delivering peroxyacetic acid tothe chiller, and a controller for the metering pump, the controller forthe metering pump being controlled by a signal from the first PAAsensing device.

Preferably, the system further comprises a unit for controlling the pHof the contents of the chiller, the unit comprising a delivery line influid communication with the chiller, a pH sensing device for sensingthe pH of fluid in the delivery line, and a flow meter for sensing therate of flow of fluid in the delivery line.

Preferably, in the system fluid output from the delivery line is inputto the first line of the device.

Preferably, the system further comprises an alkali storage tank forstoring an alkaline fluid, an alkali controller, and an alkali feed pumpfor delivering the alkaline fluid to the chiller, the alkali controllerreceiving a signal from the pH sensing device and activating the alkalifeed pump when the signal from the pH sensing device meets apredetermined condition.

In one embodiment of the system of the present invention, the source ofperoxyacetic acid provides equilibrium peroxyacetic acid. In anotherembodiment, the source of peroxyacetic acid provides nonequilibriumperoxcyacetic acid.

The present invention also provides a process for controlling theconcentration of peroxyacetic acid in a chiller employing the chillerwater sampling device. The process includes providing a continuoussample of aqueous alkaline fluid from a chiller to the first line,controlling the first valve to provide a predetermined constant flowrate of the sample to the mixing tank, mixing the aqueous fluid providedto the mixing tank, monitoring the pH of the aqueous fluid in the mixingtank, and adding acid to the aqueous fluid in the mixing tank to reducethe pH of the aqueous fluid in the mixing tank, monitoring the pH of theaqueous fluid in the fourth line, delivering aqueous fluid in the fourthline to the sixth line when the monitored pH of the aqueous fluid in thefourth line is within the working range of the first PAA sensing device;and delivering peroxyacetic acid to the chiller in response to thesignal from the third sensing device.

Preferably, the process further includes providing a second PAA sensingdevice for sensing the concentration of peroxyacetic acid in the sixthline, the second sensing device providing a second signal in response tothe concentration of sensed concentration of peroxyacetic acid signal,and comparing the signals of the first and second PAA sensing devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a chiller water sampling deviceaccording to the present invention.

FIG. 2 is a schematic illustration of a system for controlling theconcentration of peroxyacetic acid in the contents of a chilleremploying the device of FIG. 1.

DETAILED DESCRIPTION

The present invention provides a chiller water sampling device forassessing the level of peroxyacetic acid in the water of a poultrychiller, and a system employing the device for controlling theconcentration of peroxyacetic acid in the chiller water, as well as amethod for controlling the concentration of peroxyacetic acid in thechiller water.

As used in this specification and claims, “PAA” means peroxyacetic acid(also referred to a “peracetic acid).

Referring to FIGS. 1 and 2, wherein like reference numerals refer tolike elements throughout the several views, the chiller water samplingdevice 100 of the present invention includes a first line 110 for fluidcommunication with a chiller 300 (FIG. 2). A stream of chiller waterinitially flows through a first flow meter 112 for sensing fluid flowthrough the first line 110. The first flow meter 112 generates aresponsive signal over a first flow control line 113. At the end of thefirst line 110 a diverter 114 such as a “Y”-fitting, and in fluidcommunication with the first line 110, is provided to split the streamof chiller water into two streams, one of which flows into a second line116, and a third line 122. Preferably, the “Y”-fitting permits largecontaminant particles in the chiller water to flow downwards through thesecond line 116. There are fluctuations in the fluid flow through thefirst line 110, and it is desirable to provide a uniform flow rate inwhich the concentration of peroxyacetic acid can be sampled, the fluidflowing in the second line 116 passes though a second flow meter forsensing the fluid flow through the second line 116, then though a first,proportional valve 120 for controlling the fluid flow in the secondline, and subsequently to a drain 180 for discharging fluid flow fromthe device 100. A signal provided over the first flow control line fromthe first flow meter 112 and a signal provided over a second flowcontrol line 115 from the second flow meter 118 are compared by a flowcontroller 126, which is programmed to adjust the first valve 120 suchthat the fluid flow though the third line 122 is maintained at apredetermined rate, such as, for example, 0.3 gal./min (1.14liters/minute). Fluid flowing in the third line then preferably passesthrough a filter 124 such as a mesh screen to strain out residual largeparticles. The fluid flowing in the third line 122 then passes though asecond valve 128 for controlling fluid flow in the third line 122 for apurpose to be described below.

The chiller water flowing in the third line 122 discharges to a mixingtank 130 for receiving fluid flow from the third line 122 for thepurpose of adjusting the pH of the chiller water if necessary in orderthat the concentration of peroxyacetic acid be accurately assessed. Themixing tank 130 is provided with a mixer or stirrer 132 as well as avent 134.

The chiller water including the peroxyacetic acid can have a pH on thealkaline side. However, sensors for peroxyacetic acid typically have alimited pH operating range, such as from about 1 to 9. Thus, if thechiller water is more alkaline than the operating range of the PAAsensor being employed, the PAA measurement drops to zero.

Thus, a first sensing device 140 for monitoring the pH of fluid in themixing tank 130 is provided. The first sensing device 140 generates asignal responsive to the pH of the fluid in the mixing tank 130. Thesignal is applied through a first pH control line 141 to a firstmetering device or pump 144. An acid storage tank 142 is provided influid communication with the mixing tank 130 through the first meteringdevice 144, which controls fluid flow from the acid storage tank 142 tothe mixing tank 130. The first metering device 144 feeds acid from theacid storage tank 142 when the pH of the contents of the mixing tank 130rise above a predetermined level, such as a pH of 8, for the purpose oflowering the pH of the contents to a level within the working range ofthe PAA sensor to be employed. The fluid in the mixing tank 130 ispreferably maintained at a constant level 150. Should that level beexceeded, an overflow line 176 is provided for discharging the overflowfrom the mixing tank 130 to a drain 180.

A fourth line 152 is provided for discharging fluid from the mixing tank130. A second pH sensing device 154 monitors the pH of fluid flowing inthe fourth line 152. If the pH of the fluid in the fourth line 152exceeds a predetermined pH, such as a pH of 8, the second pH sensingdevice 154 generates signals which are transmitted over a second pHcontrol line 155 and a third pH control line 157, such that the fluid isdischarged through a fifth line 156 in fluid communication with thefourth line 152 and a third valve 158 for controlling fluid flow throughthe fifth line 156 to discharge fluid from the mixing tank 130 to adrain 180. In addition, a sixth line 160 in fluid communication with thefourth line 152 is also provided, as well as a fourth valve 162 forcontrolling fluid flow through the sixth line 160.

Depending on the sensed pH, the second sensing device 154 generates asignal which is applied over the second pH control line 155 forcontrolling operation of the third valve 158 and a signal applied overthe third pH control line 157 for controlling operation of the fourthvalve 162. If the pH is above a predetermined value, the third valve 158is opened and the fourth valve 162 is closed so that the chiller wateris discharged to the drain 180. If the pH is below a predeterminedvalue, the third valve 158 is closed, and the fourth valve 162 is openedto permit the chiller water to flow through the sixth line 160.

A first PAA sensing device 164 is provided, and preferably a second PPAsensing device 190, for sensing the concentration of peroxyacetic acidin fluid flowing in the sixth line 160. The first PAA sensing device 164has a predetermined operating range, and provides a PAA concentrationsignal in response to the concentration of sensed concentration ofperoxyacetic acid over a PAA signal line 165. The PAA concentrationsignal is employed to adjust the concentration of PAA in the chiller 300as described below. Preferably, signals from the two sensors 164, 190are compared, and if the two signals differ by more than a predeterminedamount, indicating malfunction, one or both PAA can be replaced.

Preferably, the device 100 further includes a seventh line 170 forproviding fluid flow, such as cleaning water, to the third line 122. Thefluid flow through the seventh line is controlled by a fifth valve 172.The seventh line 170 is in fluid communication with the third line 122between the diverter 114 and the second valve 128. In order to clean thefilter 124, fluid flow from the chiller 300 is stopped, the second valve128 is closed, and the first valve 120 is opened so that cleaning watercan flow through the filter 124 and out the second line 116 to the drain180. Further, if desired, the second valve 128 can be opened so thatcleaning water can flow through the mixing tank 130 and then to thefourth line 152. A fifth line 156 is provided in fluid communicationwith the fourth line 152, with flow through the fifth line 156 beingcontrolled by a seventh valve 168. If the third valve 158 and the fourthvalve 162 are closed, and the seventh valve 168 is opened, cleaningwater can flow from the fourth line 152 and can flow out the fifth line156 to be discharged from the device 100 to a drain 180. Similarly, aneighth line 174 in fluid communication with the sixth line 160 betweenthe fourth valve 162 and the first sensor 164 is provided. The eighthline 174 is controlled by a sixth valve 178. In order to clean thesensors 164, 190 in the sixth line 160, the fourth valve 162 can beclosed, and the sixth valve 178 can be opened in order to permitcleaning water to flow through the eighth line 174, the sixth line 160and the sensors 164, 190.

The present invention also provides a system for controlling theconcentration of peroxyacetic acid in the contents of a chiller 300. Thesystem includes the device 100, a PAA control system 400 which includesa controller 410 a source of peroxyacetic acid, such as a PAA storagetank 402 containing an equilibrium solution of PAA, a first PAA deliveryline 404 for fluid communication between the tank 402, and a PAAmetering pump 406 for delivering peroxyacetic acid to the chiller 300through a second PAA delivery line 408, and a controller 410 for themetering pump. The controller for the metering pump is preferablycontrolled by a signal from the first PAA sensing device 164.

The system of the present invention also provides a unit 200 forcontrolling the pH of the contents of the chiller 300. The unit 200includes a pH sample delivery line 206 in fluid communication with thechiller 300 for delivering a sample of the chiller contents to a pHcontrol sensing device 208 for sensing the pH of fluid in the deliveryline 206, and a pH sample flow meter 210 for sensing the rate of flow offluid in the delivery line 206. Recirculating pump 304 draws fluidthrough a recirculating line 302 from the chiller 300 and pumps thefluid back to the chiller 300 through a recirculating line 306, thusproviding in a closed recirculating path relative to the chiller 300.Delivery line 206 is in fluid communication through valve 204 and line202 with recirculating line 306, and thus the chiller 300. Preferably,the fluid output from a pH sample discharge line 212 is input to thefirst line 110 of the device 100 of the present invention. An alkalistorage tank 222 is employed for storing an alkaline fluid. The alkalinefluid, such as an aqueous solution of sodium hydroxide, is transferredto an alkali feed or metering pump 226 over a first alkali delivery line224. An alkali pump controller 230 controls the operation of the alkalimetering pump 226 for delivering the alkaline fluid over to the chiller300 over a second alkali delivery line 228. The alkali controller 230receives a signal from the pH control unit device 200 and activating thealkali feed pump 230 when the signal from the pH control unit 200 meetsa predetermined condition, such as when the pH of the chiller contentsdrops below a predetermined level.

The source of peroxyacetic acid can provide an equilibrium solution ofperoxyacetic acid. Equilibrium solutions of peroxyacetic acid can beprepared remotely from the processing plant employing the chiller, andstored until needed. Conversely, the source of peroxyacetic acid can bea device which generated peroxyacetic acid in situ and providesnonequilibrium peroxcyacetic acid.

The chiller water sampling device 100 is employed to control theconcentration of peroxyacetic acid in a chiller 300. A continuous sampleof aqueous alkaline fluid from the chiller 300 is provided to the firstline 110 of the device 100. For example, the sample can be delivered bythe pH sample discharge line 212 of the pH control unit 200. The firstvalve 120 is controlled to provide a predetermined constant flow rate ofthe sample to the mixing tank 130, such as 0.3 gallons/minute (1.14liters/minute). The aqueous fluid in the mixing tank 130 is mixed,preferably continuously using a mechanical stirring device or mixer 132.The pH of the aqueous fluid in the mixing tank 130 is monitored with thefirst sensing device 140, and if the pH of the aqueous fluid exceeds apredetermined value, the acid addition flow controller 126 causes acidstored in the acid storage tank 142 to be added by the first meteringdevice 144 to the aqueous fluid in the mixing tank 130 to reduce the pHof the aqueous fluid in the mixing tank 130. Since peroxyacetic acidsensors have a limited range of pH in which they can operate accurately,and because the pH of aqueous fluid in the chiller may exceed theoperating range of the peroxyacetic acid sensor, the pH of a sample ofaqueous fluid from the chiller 300 must be reduced to within theoperating range of the peroxyacetic acid sensor in order to accuratelyassess the level of peroxyacetic acid in the chiller 300. In order toprotect the peroxyacetic acid devices 164, 190, the pH of the aqueousfluid leaving the mixing tank 130 in the fourth line 152 is monitored bythe second sensing device 154. If the pH of the sample has beensufficiently reduced, the third valve 158 is closed and the fourth valve162 is opened, and the aqueous fluid sample in the fourth line 152 isdelivered to the sixth line 160 when the monitored pH of the aqueousfluid in the fourth line is within the working range of the PAA sensingdevices 164, 190. The measured level of peroxyaceticacid acid in thesample is then used to control the addition of peroxyacetic acid to thechiller 300. A PAA control signal is generated by the sensing device164, and peroxyacetic acid is delivered to the chiller 300 in responseto the signal from the first PAA sensing device.

Preferably, the second sensing device is provided for sensing theconcentration of peroxyacetic acid in the sixth line 160. The second PAAsensing device 190 provides a second signal in response to theconcentration of sensed concentration of peroxyacetic acid signal. Thesignals from the first PAA sensing device 164 and the second sensingdevice 190 can be compared. If the levels measured by the two devicesdiffer by greater than a predetermined amount, indicating a defective ordamaged sensor, that sensor can be replaced.

Various modifications can be made in the details of the variousembodiments of the apparatus and method of the present invention, allwithin the scope and spirit of the invention as defined by the appendedclaims.

The invention claimed is:
 1. A chiller water sampling device, the deviceincluding: a first line configured to enable a flow of discharged fluidfrom a chiller; a first flow meter for sensing fluid flow through thefirst line; a diverter in fluid communication with the first line fordividing the fluid flow from the first line into a second line and athird line; a second flow meter for sensing fluid flow through thesecond line; a first valve for controlling fluid flow through the secondline; the second line discharging fluid flow from the device; a secondvalve for controlling fluid flow through the third line; a mixing tankfor receiving fluid flow from the third line; an acid storage tank influid communication with the mixing tank; a first metering device forcontrolling fluid flow from the acid storage tank to the mixing tank; afirst pH sensing device for monitoring the pH of fluid in the mixingtank, the first sensing device generating a first signal responsive tothe pH of the fluid in the mixing tank, the first signal being appliedto the first metering device for controlling fluid flow from the acidstorage tank to the mixing tank; a fourth line for discharging fluidfrom the mixing tank; a second pH sensing device for monitoring the pHof fluid flowing in the fourth line; a fifth line in fluid communicationwith the fourth line for discharging fluid from the device; a thirdvalve for controlling fluid flow through the fourth line; a sixth linein fluid communication with the fourth line for discharging fluid fromthe device; a fourth valve for controlling fluid flow through the sixthline; the second pH sensing device generating a second signal forcontrolling operation of the fourth valve and a third signal forcontrolling operation of the third valve such that when the pH sensed bythe second pH sensing device is above a predetermined value, the thirdvalve is open and the fourth valve is closed, and when the pH sensed bythe second pH sensing device is below the predetermined value, the thirdvalve is closed and the fourth valve is opened; and a first PAA sensingdevice for sensing the concentration of peroxyacetic acid in fluidflowing in the sixth line, the first PAA sensing device having anoperating range, and providing a signal in response to the concentrationof sensed concentration of peroxyacetic acid signal.
 2. A deviceaccording to claim 1 further comprising a filter in the third line forfiltering non-fluid material from fluid flowing from the diverter to thesecond valve.
 3. A device according to claim 2 further comprising aseventh line for providing fluid flow to the third line, fluid flowthrough the seventh line being controlled by a fifth valve, the seventhline being in fluid communication with the third line between thediverter and the second valve.
 4. A device according to claim 1 furthercomprising an overflow line, the overflow line being in fluidcommunication with the mixing tank for discharging fluid from thedevice, the overflow line being positioned to discharge fluid from themixing tank above a predetermined fluid level in the mixing tank.
 5. Adevice according to claim 1 further comprising a second PAA sensingdevice for sensing the concentration of peroxyacetic acid in the sixthline.
 6. A device according to claim 1 further comprising an eighth linefor providing fluid flow to the sixth line, the fluid flow in the eighthline being controlled by a sixth valve, the eighth line being in fluidcommunication with the sixth line between the fourth valve and the firstPAA sensing device.
 7. A device according to claim 1 wherein the firstflow meter generates a first flow control signal, the second flow metergenerates a second flow control signal, and the first valve is aproportional valve, the device further including a controller forcomparing the first signal and the second signal, and generating acontrol signal for the proportional valve, such that the flow throughthe third line is maintained at a predetermined flow rate.
 8. A systemfor controlling the concentration of peroxyacetic acid in the contentsof a chiller, the system comprising a device according to claim 1arranged to receive fluid discharged from a chiller, a source ofperoxyacetic acid, a metering pump for delivering peroxyacetic acid fromthe source of peroxyacetic acid to the chiller, and a controller for themetering pump, the controller for the metering pump being controlled bya signal from the first PAA sensing device.
 9. A system according toclaim 8 further comprising a unit for controlling the pH of the contentsof the chiller, the unit comprising a pH sample delivery line in fluidcommunication with the chiller for delivering fluid from the chiller, apH sensing device for sensing the pH of fluid in the pH sample deliveryline, and a flow meter for sensing the rate of flow of fluid in thedelivery line.
 10. A system according to claim 9 wherein the deliveryline is in fluid communication with the first line of the device.
 11. Asystem according to claim 9 further comprising an alkali storage tankfor storing an alkaline fluid, an alkali controller, and an alkali feedpump for delivering the alkaline fluid to the chiller, the alkalicontroller receiving a signal from the pH sensing device which sensesthe pH of the fluid in the pH sample delivery line, and activating thealkali feed pump when the signal from the pH sensing device meets apredetermined condition.
 12. A system according to claim 8 wherein thesource of peroxyacetic acid comprises a tank containing equilibriumperoxyacetic acid.
 13. A system according to claim 8 wherein the sourceof peroxyacetic acid comprises a device for generating nonequilibriumperoxyacetic acid.
 14. A process for controlling the concentration ofperoxyacetic acid in a chiller employing a device according to claim 1,the process comprising: providing a continuous sample of aqueousalkaline fluid from a chiller to the first line, controlling the firstvalve to provide a predetermined constant flow rate of the sample to themixing tank; mixing the aqueous fluid provided to the mixing tank;monitoring the pH of the aqueous fluid in the mixing tank, and addingacid to the aqueous fluid in the mixing tank to reduce the pH of theaqueous fluid in the mixing tank; monitoring the pH of the aqueous fluidin the fourth line, delivering aqueous fluid in the fourth line to thesixth line when the monitored pH of the aqueous fluid in the fourth lineis within the working range of the first PAA sensing device; anddelivering peroxyacetic acid to the chiller in response to the signalfrom the third sensing device.
 15. A process according to claim 14,further comprising providing a second PAA sensing device for sensing theconcentration of peroxyacetic acid in the sixth line, the second sensingdevice providing a second signal in response to the sensed concentrationof peroxyacetic acid signal, and comparing the signals of the first andsecond PAA sensing devices.